THIS IS A SHANNON AWARD PROVIDING PARTIAL SUPPORT FOR THE RESEARCH PROJECTS THAT FALL SHORT OF THE ASSIGNED INSTITUTE'S FUNDING RANGE BUT ARE IN THE MARGIN OF EXCELLENCE. THE SHANNON AWARD IS INTENDED TO PROVIDE SUPPORT TO TEST THE FEASIBILITY OF THE APPROACH; DEVELOP FURTHER TESTS AND REFINE RESEARCH TECHNIQUES; PERFORM SECONDARY ANALYSIS OF AVAILABLE DATA SETS; OR CONDUCT DISCRETE PROJECTS THAT CAN DEMONSTRATE THE PI'S RESEARCH CAPABILITIES OR LEAD ADDITIONAL WEIGHT TO AN ALREADY MERITORIOUS APPLICATION. THE APPLICATION BELOW IS TAKEN FROM THE ORIGINAL DOCUMENT SUBMITTED BY THE PRINCIPAL INVESTIGATOR. The malignant progression of melanoma is often accompanied by overexpression of the low-affinity p75 neurotrophin receptors. The most aggressive melanomas also frequently exhibit brain colonization properties. I am using brain-colonizing melanoma variants that express p75 in association with metastatic potential as a model system for analyzing the effects of neurotrophins on metastatic behavior. My working hypothesis is that p75-mediated trophism may promote the invasion and survival of melanoma cells in the neurotrophin rich microenvironment of the brain. I have most recently shown that neurotrophins affect the metastatic properties of human melanoma cells by (1) enhancing malignant melanoma chemoinvasion and (2) promoting malignant melanoma cell survival. Importantly, the low-affinity p75 receptor expression by certain brain- colonizing human melanomas directly correlates with their metastatic potentials. These observations prompted me to develop the following specific aims: (1) I will determine the exact roles of p75 in invasion and survival by modifying the expression of p75 in melanoma cells using: a) fluorescence activated cell sorting; b) p75 antisense oligo-nucleotides; c) p75 expression constructs; or d) genetic ablation of p75 in mouse melanoma. (2)1 will determine the relative roles of the various neurotrophins in promoting invasion and survival of melanoma cells in vitro. These studies will involve Transwell(TM) invasion assays and survival assays developed in my laboratory to examine the effects of neurotrophin-3, brain-derived neurotrophic factor and neurotrophin-4/5 on melanoma invasion and survival. (3) Depending on the success of the in vitro studies, I will examine the role of p75 during invasion and survival of selected human melanoma variants following injection into nu/nu mice. Animals will be sacrificed and tumors reestablished in culture as well as paraffin embedded for immunohistochemical characterization of p75. My results are the first to suggest the importance of trophic mechanisms in the progression of metastatic melanoma. Similar examples of trophic survival mechanisms may occur during tumor dormancy, cell survival in the necrotic regions of tumors, and cryptic survival of micrometastases. Further understanding of trophic mechanisms in melanoma progression may provide an important basis for the future research, discoveries and therapeutic approaches for not only malignant melanoma but also other malignant diseases.